With the recent dramatic increase in demand in communications, high-capacity, high-speed photonic network applications have spread to the extent that even metro access systems are accessible to subscribers.
An optical module provided with a semiconductor optical amplifier (SOA) (SOA module) has a dramatically simplified structure compared to the currently popular optical module provided with an optical fiber amplifier (optical fiber amplifier module). The optical module (SOA module) allows for greater miniaturization and price reduction, and application to the next-generation access network and data communications is under consideration.
An SOA module may be equipped with, for example, an input-side optical fiber, an input-side lens system, an SOA chip, an output-side lens system, and an output-side optical fiber. Signal light is input to the input-side optical fiber, optically coupled to the SOA chip through the input-side lens system, amplified in the SOA chip, optically coupled to the output-side optical fiber through the output-side lens system, and then output from the output-side optical fiber.
In an optical network, the signal light input to the SOA module is not always polarized in the same way, and the polarization state varies with time.
Therefore, for the SOA module having input signal light with a constant intensity to always output signal light with a constant intensity, the SOA module needs to have an optical gain that does not vary with the polarization of the input signal light.